Multi-layer interconnect

ABSTRACT

Methods and apparatus for increasing the yield achieved during high density interconnect (HDI) production. In particular, processes in which panels are tested to identify good cells/parts, good cells are removed from the panels, and new panels created entirely of identified/known good cells allow increases in the number of layers used in a HDI without incurring the decrease in yield normally associated with such a layering process.

FIELD OF THE INVENTION

The field of the invention is multi-layer substrates/interconnects.

BACKGROUND OF THE INVENTION

An integrated circuit (IC) package is a housing which environmentallyprotects the IC, facilitates testing of the IC, and facilitates the useof the IC in high-yield assembly processes. Such a package functions toprotect an IC from mechanical and environmental stresses andelectrostatic discharge. It also functions to provide a mechanicalinterface for testing, burn-in, and interconnection to a higher level ofpackaging such as a circuit card.

In many IC packages a substrate acts as an interconnecting layer betweenthe terminals or pads on the IC, and the connectors or leads of thepackage. The substrate is typically mechanically and electricallycoupled to both the IC and the package leads. The substrate may be madefrom a ceramic or organic material, may be rigid or flexible, and maycomprise a single layer or multiple layers laminated together.

As IC technology progresses, there is a growing need for higher densityinterconnecting layers. The process used by the printed circuit boardindustry to build high density interconnects typically starts withproviding a large multi-layered printed circuit board core having 2-6layers with drilled and plated through holes. Individual parts arestepped and repeated on the core to produce a panel of parts. A highdensity interconnect (HDI) comprises multiple panels/layers. HDI layersare typically either added sequentially, layer by layer or layers aremade individually and then laminated in mass.

Each layer/panel of an HDI generally has good and bad parts. Thepercentage of the total number of parts which are good is typicallyspecified as percentage yield. For a single panel/layer it is notuncommon to achieve a yield of 90%. However, since each layer has lessthan 100% yield, and since bad parts tend to be distributed randomlythroughout the panel, each layer added to an HDI panel tends to decreasethe number of good parts on, and thus the yield of, the panel. Thus, atwo layer interconnect comprising two 90% panels may have a yield of81%, i.e. 81% of the individual parts/cells on the panel are good. Athree layer interconnect may have a yield of 73%, four layers 66%, andfive layers 60%. This decrease in yield as the number of layers isincreased undesirable. Thus, there is a continuing need to develop newforms and new method for producing high density interconnects.

SUMMARY OF THE INVENTION

The present invention is directed to methods and apparatus forincreasing the yield achieved during high density interconnect (HDI)production. In particular, processes in which panels are tested toidentify good cells/parts, good cells are removed from the panels, andnew are panels created entirely of the identified/known good cells allowincreases in the number of layers used in a HDI without incurring thedecrease in yield normally associated with such a layering process.

Various objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of preferred embodiments of the invention, along with theaccompanying drawings in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a portion of a multi-celled assemblyembodying the invention.

FIG. 2 is a perspective view of a portion of a multi-celled assemblyembodying the invention.

FIG. 3 is a perspective view of a layer-pair according to the disclosedinvention.

FIG. 4 is a top view of a panel of layer-pairs according to thedisclosed invention.

FIG. 5 is a perspective view of a bond-ply according to the disclosedinvention.

FIG. 6 is a top view of a panel of bond-plys according to the disclosedinvention.

FIG. 7a is a perspective view of a portion of a multi-celled assemblyembodying the invention.

FIG. 7b is a detailed view of a joint between two cells of FIG. 7a.

FIG. 8 is a top view of the panel of FIG. 4 having a phantomcutting/singulation pattern superimposed.

FIG. 9 is a top view of the panel of FIG. 6 having a phantomcutting/singulation pattern superimposed.

FIG. 10 is an exploded view of a stack/cell according to the disclosedinvention.

DETAILED DESCRIPTION

Referring to FIG. 1, an assembly 1 of HDI cells 5 can be seen to be amulti-celled assembly comprising a plurality of cells 5 wherein eachcell 5 is bound to adjacent cells 5 and adhesive material 22. Cells 5are preferably laid out horizontally to form a rectangular panel or alinear strip of interconnected cells, but may have other forms as well.If formed into a rectangular panel, cells 5 are preferably laid out inrows and columns with the number of cells in each row preferred to bebut not necessarily equal to the number in the other rows and the numberof cells in each column preferred to be but not necessarily equal to thenumber in the other columns. Although not limited in number orparticular layout, it is contemplated that panels having a total of Tcells arranged in rows containing X cells and columns containing Y cellswhere (T, X, Y) are (4, 2, 2), (4, 1, 4), (7, 1, 7), (8, 2, 4), (9, 3,3), (9, 1, 9), (12, 3, 4), (16, 4, 4), (16, 1 6), (25, 5, 5), (36, 6, 6)may be particularly desirable. If formed into linear strips it iscontemplated that 1 or more parallel rows having a large number ofcolumns may be rolled for ease in later transportation, handling andprocessing.

Cells 5 may each have unique shapes, or, as shown in FIG. 1, to comprisea uniform interlocking shape. However, it is currently preferred thatcells 5 comprise uniform rectangular shapes. It is contemplated thatuniformity between cells is advantageous when forming new multi-celledunits from the good cells. It is also contemplated that making theshapes interlocking helps to prevent untimely separation of the cells.However, with an appropriate choice of adhesive material 22non-interlocking rectangular shapes are sufficient, and alternativeshapes such as ovals may be chosen.

Referring to FIG. 2, cells 5 can be seen to comprise layer-pairs 10 andbond-ply layers 20. Although cells comprising a single layer-pair 10 arecontemplated, the assembly and methods disclosed herein are thought tobe particularly advantageous when the cells 5 are stacks of alternatinglayer-pairs 10 and bond-ply layers 20 and the cells/stacks 5 havelayer-pairs 10 on both ends of the stack.

Referring to FIG. 3, layer-pairs 10 are preferred to comprise a layer ofpolyimide film 14 bearing conductive patterns 11 on its upper and lowersurfaces. The “pair” portion of the term “layer-pair” indicates that twoopposing sides of the base layer bear conductive patterns. Lesspreferred embodiments may utilize layer-pairs having non-polyimide baselayers, or may use layers having conductive patterns on only one side(i.e. a substrate having a conductive pattern on one side and ametallized but relatively unpatterned opposing side such as a groundplane) in place of one or more layer-pairs. Layer pairs 10 are alsopreferred to include alignment/tooling pin holes 19.

Layer-pairs 10 are preferably formed by the following process: providinga panel of polyimide film, laser drilling through holes/vias in thepanel; sputtering chromium and copper layers onto the panel; andproducing conductive patterns on opposing sides of the panel bysubmitting the sputtered surfaces to a photolithographic process.Referring to FIG. 3, this process can be used to produce a plurality ofpanels 2, each panel containing multiple layer-pairs 10 interconnectedby the common polyimide film base layer 14 of the layer pairs 10. Theindividual layer-pairs 10 on each panel are then inspected and/orelectrically tested to identify good parts.

Referring to FIG. 5, bond-ply layers 20 are preferred to comprise 1non-adhesive layer 24 between adhesive layers 22, and to have conductivevias 26 and alignment/tooling pin holes 29 passing through the layersfrom one side to the other. The materials used in the adhesive andnon-adhesive layers may differ as it is preferred that the non-adhesivematerial be chosen to provide sufficient stability and support while theadhesive is chosen to have desirable adhesive and flow characteristics.In preferred embodiments, the conductive vias 26 passing through layers24 and 26 comprise a conductive metallic ink filled hole passing throughthe non-adhesive layer 24 and terminating in a pair of posts or nubbinsextending into and possibly through the opposing adhesive layers 26. Itis contemplated that alternative embodiments may use something otherthan conductive metallic ink filled through holes to establishconductive paths 26 through the bond-play layer 20. It is alsocontemplated that bond-ply layers 20 which, at least prior tolamination, do not include conductive paths 26 extending through themmay be used if alternative methods are used to establish electricalconductivity between layer-pairs 10.

Referring to FIGS. 7a and 7 b, when stacked, each adhesive layer 22 ofthe bond-ply layers 20 of Figures will mate with a surface of alayer-pair 10 bearing a conductive pattern 11. Conductive pattern 11will typically comprise a raised portion of the surface of layer-pair10. If one were to view a “slice” of the layer-pair which included onlyone of its conductive patterns it would be seen that the volume of theslice is only partially filled by the conductive pattern, anddifferences in conductive patterns would result in such a slice havingmore or less non-filled volume. When stacked, the adhesive layer 22 ofthe bond-ply layers 20 will typically flow between the raised portionsof the conductive pattern 11 to fill this previously non-filled volume.The adhesive has to fill the gaps where the copper isn't. It iscontemplated that, because different patterns have differing amounts of“non-filled volume”, that the volume of material included in aparticular adhesive layer 22 may be adjusted to correspond, at least inpart, to the amount of “non-filled volume” of the mating layer-pairsurface. In such embodiments, the volume of adhesive material in any twoof the adhesive layers 22 of the bond-ply 20 may differ.

Referring again to FIG. 5, although the choice of materials for use inthe adhesive layers 22 is largely unrestrained, it is preferred that theadhesive layers comprise a polymer preferably based on high Tgchemistries. It is also preferred that a transient liquid phasesintering conductive ink be used in forming conductive paths 26.

Bond-ply layers 20 are preferably formed by the following process:providing an adhesive coated base layer (i.e. a having a non-adhesivelayer sandwiched between two adhesive layers), the outer surfaces of theadhesive layers being covered by a protective release sheets 27; laserdrilling through holes/vias into the protected base layer; and pressurefilling the through holes with conductive ink. Release sheets 27 arepreferably polymer based, but alternative materials such as copper maybe utilized as well. Referring to FIG. 6, this process can be used toproduce a plurality of bond-ply panels 3, each panel containing multiplebond-plys 20 interconnected by the base layer 24 of FIG. 5. Theindividual bond-plys 20 on each panel are then inspected and/orelectrically tested to identify good parts.

It is contemplated that the pressure fill step may be improved in anumber of ways including orienting the bond-ply layer during thepressure fill process such that the process fills the through holesthrough either the laser entry or exit points of the through holes;optically registering the stencil used in the fill process rather thanmechanically (which is the predominant method used by the industry);ramping up (i.e. slowly increasing) the pressure used in the pressurefill process; using a repeated and preferably automated apply, fill, andrelease cycle in applying the stencil and/or ink to the bond-ply layer,fill the vias, and release/remove the stencil from the bond-ply layer;and using a porous ceramic chuck with a layer of z-permeable paperbetween the chuck and the lamination plate.

A method for producing a HDI as previously described comprises providingknown good layer-pair and bond-ply layers, forming stacks of alternatinglayers of known good layer-pair and bond-ply layers, and laminating thestacks so as to form them into a panel of HDIs.

Referring to FIGS. 8 and 9, providing known good layer-pairs 10 andbond-ply layers 20 may comprise providing layer-pair and bond-ply panels(2 and 3), each panel (2 or 3) comprising multiple layer-pairs 10 orbond-plys 20, testing the individual layer-pairs 10 and bond-plys 20,and singulating/breaking up the panels into individual parts with onlythe good parts being used in later steps. Singulation of individualparts may be accomplished by any means including manually cutting theparts from the panel as well as through the use of automated methods. Itis contemplated that laser cutting or the use of a steel ruled die wouldbe advantageous. In some embodiments, the remains of the original panelsmay be retained to create a framework for use in forming the individualparts back into a panel. The phantom lines of FIGS. 8 and 9 show onepossible pattern for use in singulating panels 2 and 3.

Referring to FIG. 10, release sheets 30 are added to a top and a bottomlamination plate, the layer-pair and bond-ply layers 10 and 20 are pressfitted onto tooling pins 41 of the bottom lamination plate 40, the toplamination plate is added, and the resulting sandwich is vacuumlaminated in a press to form panels of known good parts. The bottomlamination plate 40 is preferred to hold all the pieces of the panel (2or 3).

After the final/top lamination plate is added, the stacks are pressed tocause adhesive layers 22 to flow and to fill in the empty spaces betweenconductive patterns 11 and between cells/stacks 5. After the adhesivelayers have been caused to flow and while maintaining pressure on thestacks 5, everything is then heated to cure the adhesive portions and tocause sintering of the conductive ink After heating/curing, at leastsome of the cured portions interconnect the stacks so as to form apanel. It is contemplated that interlocking the pieces prior topanelization helps alleviate problems of brittleness. In a lesspreferred process, the base material frameworks left after singulationof the layer-parirs and bond-plys are used to help fill the gap betweenstacks. During panelization, there a slight increase in the distancebetween cells/pieces.

HDI formation, in addition to the steps previously described, mayinclude additional steps such as, but not necessarily limited to, e-lessnickel plating; soldermasking; e-less gold plating; stack singulation;electrical test; and final inspection steps.

Thus, specific embodiments of HDIs and methods for forming HDIs havebeen disclosed. It should be apparent, however, to those skilled in theart that many more modifications besides those already described arepossible without departing from the inventive concepts herein. Theinventive subject matter, therefore, is not to be restricted except inthe spirit of the appended claims. Moreover, in interpreting both thespecification and the claims, all terms should be interpreted in thebroadest possible manner consistent with the context. In particular, theterms “comprises” and “comprising” should be interpreted as referring toelements, components, or steps in a non-exclusive manner, indicatingthat the referenced elements, components, or steps may be present, orutilized, or combined with other elements, components, or steps that arenot expressly referenced.

What is claimed is:
 1. A multi-celled assembly comprising: a pluralityof horizontally adjacent cells wherein each cell comprises at least onebase material layer and at least one conductive pattern; the adjacentcells of the assembly being bound together solely by an adhesivematerial.
 2. The assembly of claim 1 wherein the composition of theadhesive material differs from the composition of the at least one basematerial layer of the cells.
 3. The assembly of claim 2 wherein the atleast one base material layer comprises a polyimide film.
 4. Theassembly of claim 1 wherein: each cell is a stack of alternatingbond-ply and layer-pair layers, the layer-pair layers comprising the atleast one base material layer and at least one conductive pattern. 5.The assembly of claim 4 wherein: during formation of the assembly, thebond-ply layers are provided in a form comprising at least one adhesivelayer; during formation of the assembly, inclusion of the bond-plylayers in the stacks results in portions of the adhesive layersinterconnecting the stacks; during formation of the assembly but afterthe stacks are interconnected by portions of the adhesive layer, theinterconnecting portions of the adhesive layer are cured.
 6. Theassembly of claim 1 wherein the assembly is produced by: providing aplurality of known good layer-pairs and bond-ply members; forming theknown good layer-pairs and bond-ply members into adjacent stacks;interconnecting the adjacent stacks to form a multi-celled unit.
 7. Theassembly of claim 6 wherein each of the layer-pairs comprises apolyimide base layer having conductive patterns on two opposing sides.8. The assembly of claim 6 wherein each known good bond-ply membercomprises at least two adhesive layers and one non-adhesive layer. 9.The assembly of claim 1 wherein the assembly is produced by: providing amulti-celled unit comprising a plurality of cells joined together by atleast one common interconnecting layer wherein each cell comprises atleast one conductive trace, pad or via; identifying good cells havingdesirable characteristics; separating each good cell from the commoninterconnecting layer and forming a new multi-celled unit from the goodcells.
 10. The assembly of claim 9 wherein the step of coupling the goodcells together to form a new multi-celled unit comprises the steps of:positioning the cells of the group of good cells adjacent to each other;providing a corresponding bond-ply layer for each cell, wherein thebond-ply layer comprises at least one adhesive layer and at least onenon-adhesive layer; stacking each bond-ply layer onto its correspondingcell to form a stack and thus converting the group of adjacent goodcells into a group of adjacent stacks; applying sufficient pressure tothe adjacent stacks to force portions of the adhesive layers of eachstack into contact with adjacent stacks; curing the adjacent stacks tocure the adhesive layers.
 11. The assembly of claim 10 wherein thebond-ply layers have a non-adhesive layer between a first adhesive layerand a second adhesive layer.
 12. The assembly of claim 11 wherein thevolume of adhesive material in the first adhesive layer differs from thevolume of adhesive material in the second adhesive layer.
 13. Theassembly of claim 12 wherein the volume of adhesive material in at leastone adhesive layer of a bond-ply layer is adjusted based on the volumeof space to be filled between the bond-ply layer and its correspondingcell and between the bond-ply layer and one or more adjacent stacks. 14.A multi-celled assembly comprising a plurality of horizontally adjacentcells wherein: each cell is a stack of alternating bond-ply and knowngood layer-pair layers; the known good layer-pair layers each compriseat least one base material layer and at least one conductive pattern;the bond-ply layers each comprise an adhesive material wherein thecomposition of the adhesive material differs from the composition of thebase material layers, each bond-ply layer is sandwiched between twoknown good layer-pair layers; and the adjacent cells of the assembly arebound together solely by the adhesive material of the bond-ply layers.